MLA

Horowitz, Vladimir, 1903-1989. Sergei Rachmaninoff. Box 18, folder 248. 1928-1965. https://collections.library.yale.edu/catalog/32212228.

APA, 6th edition

Horowitz, Vladimir, 1903-1989. (["Box 18, folder 248"])(1928-1965)[Sergei Rachmaninoff]. https://collections.library.yale.edu/catalog/32212228.